Motor graders have a longitudinal main frame which has a dirigible wheel assembly at its forward end, an operator's cab at its rearward end portion, and a traction chassis for the motor and power train behind the cab. The motor grader blade is suspended from the main frame by means of a circle draw bar and a circle. The circle draw bar has its front end connected to the front of the main frame by a ball and socket connection, while the rearward portion of the circle draw bar is suspended from the main frame by hydraulic cylinder and piston means which permit the draw bar to swing in a vertical plane about its front end.
The circle is mounted on the rearward portion of the circle draw bar for rotation about a vertical axis, and there is a driving interconnection between a motor on the circle draw bar and a ring gear on the circle to effect such rotary motion of the circle.
The grader blade is mounted upon the circle so that rotation of the circle changes the angle of the blade with reference to the path of travel of the grader, while swinging the circle draw bar in a vertical plane about its forward end changes the vertical position of the grader blade with reference to the ground.
In addition, the grader blade is mounted on a horizontal axis so that it may be tipped with respect to the circle by hydraulic cylinder and piston means to change the angle of attack of the blade and it may also be shifted endwise in its mounting.
The hydraulic cylinder and piston units which have heretofore been used to control the tilt of the grader blade assembly have been subject to damage from masses of earth and rocks pushed up by the grader blade moldboard. In addition, the necessity for connecting the cylinder of a hydraulic cylinder and piston unit to the circle with the rod connected to the blade carrying means requires that the head end of the cylinder be mounted to pivot about a transverse axis, and elimination of excessively close manufacturing tolerances for such heavy equipment make it highly desirable that the head end of the cylinder be rotatable about an upright axis as well. However, double trunnion mountings are quite large and clumsy, and cannot be adequately protected against damage from dirt and dust in the very difficult environment in which such hydraulic cylinder units are used.
Typical mountings of hydraulic cylinder and piston units in heavy earth moving equipment are disclosed in U.S. Pat. Nos. 3,311,026, 3,521,782 and 3,631,930. Also of interest are U.S. Pat. Nos. 3,147,671 and 3,683,754.